The present invention relates to NVIS-compliant instruments and a method for manufacturing same.
Illumination of cockpit instruments is achieved by the use of different lighting technologies. They include electroluminescent lamps, incandescent lamps and Light Emitting Diodes (LEDs).
These different illumination technologies are used both in the commercial and military avionics industry. Each of the industry has different illumination color requirements covered by various government specifications. Some military or paramilitary application, including airborne but not limited to, require specific lighting requirements due to their usage in night operation. During these operations, night vision goggles are used by flight crews to enhance terrain visibility outside the aircraft in low visibility conditions. The cockpit illumination must be such that it does not emit energy that could interfere with the infrared sensitive night vision goggles or other night vision equipment. Illumination adhering to this standard is known as NVIS compliant light. The night vision goggles used in military aircrafts are responsive to low light level intensities, typically in the 625 nm to 920 nm band, including the red and infrared portions of the spectrum. The devices employ high gain electronic image intensifiers that are sensitive to light in the near-infrared and infrared regions. If a high level of infrared output is emitted by the illumination system and reaches the observer, a phenomenon known as blooming occurs, whereby the observer suffers from night vision impairment to an unacceptable degree. The infrared emissions from the cockpit illumination must be removed or eliminated to a degree that there is no interference with the use of the night vision equipment. At the same time, the illumination must be such that it provides sufficient brightness for direct viewing with the unaided adapted eye. Accordingly, the instrument emissions in the infrared region should be minimized, without affecting the portion of the visible spectrum to which the human eye is most sensitive.
Cockpits are designed and manufactured to meet the military quantitative requirements for energy distribution and color as defined in government specification. In the past, these requirements have been achieved by different filtering techniques using glass or plastic or a combination thereof. The need for requirements compliance has increased manufacturing costs given the optical requirements and the state of the art. Integration of filtering material into a single component has been claimed in U.S. Pat. No. 5,686,786 for incandescent based technology.
Illumination requirements have been achieved by using electroluminescent lamps, incandescent lamps and LEDs as light source. The radiance and chromaticity requirements as described above have required the development of filtering materials. In fact, the large energy spectrum of the incandescent lamps required absorbing filters of different materials and shapes. Such filters are designed for high absorption of the longer wavelengths in the infrared region of the spectrum and high transmission at shorter wavelengths in the visual region. However, the overall efficiency after such filters is relatively low, as they absorb significant amounts of energy in the visual spectrum, lowering the overall brightness.
The use of electroluminescent lamps required similar filtering material despite the narrower energy distribution of the phosphors used in order to eliminate small quantity of energy present above 600 nm.
The introduction of Blue LED dies lead to much advancement in wide spectrum LED based illumination. As an example, recent developments by Nichia of Japan with the introduction of product such as NSPW310AS, described in U.S. Pat. No. 6,069,440 to Shimizu et al., that added Yttrium Aluminum Garnet doped with cerium to the Blue LED package, has provided a promising alternative to the incandescent and electroluminescent based technologies. The light emitting device described above is coated with a phosphor such that it converts the blue emission of the light emitting diode into a very broad spectrum. Other similar approaches combining various phosphors and excitation wavelengths are also available.
By nature, the LED has proven to be extremely reliable compared to incandescent lamps when exposed to vibration and thermal cycling. The LED has also demonstrated longevity much greater than the electroluminescent and incandescent lamps. Moreover, the LED requires less energy for similar brightness output.
Despite this recent improvement, the LED, given its energy spectrum also requires the use of external filtering component in order to absorb energy in the infrared and red spectrum. In the prior art, this external filtering component or material is external to the LED. The use of filtering material in this spectrum region, usually above 700 nm, impacts the efficiency and significantly increases the cost associated with the manufacturing of the final assembly. In practice, the filtering component is made of polycarbonate and requires the use of expensive metallic dyes to sustain high molding temperatures. In general, the filtering component has to be bonded and an optical seal between the LED and the filtering material is required in order to avoid leakage of unfiltered light which would not be compliant with night vision imaging system standards. In short, the fact of not having a light source with low radiance and the required chromaticity increases overall cost while reducing the optical efficiency. There exists a need therefore for an illumination source that is both compliant to night vision imaging system requirements and incurs low manufacturing costs.
Accordingly, it is an object of this invention to provide an assembly of light emitting diodes combining to produce light compliant with a night vision imaging system standard, comprising at least one green light emitting diode die having an emission of a first dominant wavelength, at least one blue light emitting diode die having an emission of a second dominant wavelength, an electronic instrument component containing the green light emitting diode die and the blue light emitting diode die arranged to provide a mixing of said green light emitting diode emission and said blue light emitting diode such as to achieve a desired spectral response. The assembly is such that a sufficient quantity of said green light emitting diode emission is mixed with a sufficient quantity of said blue light emitting diode emission such that said resulting spectral response allows operator to perceive an essentially green light of chromaticity and radiance characteristics compliant to the night vision imaging system standard. The combination of such LED dies increases the optical efficiency and allows significant cost reduction in both material and labor compared to the existing technologies and processes.
It is another object of this invention to provide an electronic component for use in a night vision imaging system environment comprising a printed circuit board assembly comprising a light source having an emission non compliant to the night vision imaging system standard, a conformal coating covering the printed circuit board assembly, including an absorbing agent, for filtering quantities of energy of the emission, such that the infrared emission of the printed circuit board assembly is filtered by the absorbing agent.
Yet another object of this invention is to provide a method of manufacturing a printed circuit board assembly for use in a night vision imaging system environment comprising the steps of providing a printed circuit board assembly having infrared energy emissions, coating the printed circuit board assembly with a conformal coating including an absorbent agent, for filtering the infrared energy emissions and installing the printed circuit board assembly in an instrument panel such that the emissions are compliant to night vision applications for radiance and chromaticity .